This is a revised application for renewal of a long-standing Program Project. The focus of the Program Project has been on the role of the peripheral and central nervous system in pain mechanisms. Animal models of human pain states are used so that experimental manipulations can be employed to provide evidence for pathophysiological mechanisms of pain or potential improvements in therapy, hence translational capability would be heightened. An emerging concept in mechanisms underlying persistent pain is that elevated intracellular levels of reactive oxygen species (ROS) play a critical role in peripheral and central sensitization. The overall hypothesis of this PPG is that ROS themselves act as signaling molecules imposed upon the cell signaling pathways involved in sensitization processes. Three projects are proposed, each project is designed to reveal specific aspects of ROS involvement in central sensitization and persistent pain. Project 1 examines the role of ROS in central neuropathic pain. This project hypothesizes that chronic central neuropathic pain associated with spinal cord injury is composed of two components: central and peripheral sensitization. The role of ROS in both of these components will be examined using in vivo and in vitro preparations in rats. Project 2 is concerned with the critical role of ROS in central sensitization in the spinal cord using a capsaicin induced hyperalgesia model in mice (including mutant mice). This project examines ROS metabolism in the spinal cord with the emphasis on the role of superoxide dismutase and the steps in which ROS sensitize dorsal horn neurons. Project 3 investigates the role of ROS in the sensitization of neurons in both the spinal cord and the central nervous system (amygdala) in visceral pain plasticity using a colitis pain model in rats. These projects will be interlinked by three cores: Administrative, ROS Analytical, and Imaging Cores. Thus, sum of all projects interlinked by by the supporting cores will provide data showing the benefits of limiting or eliminating the increases in ROS as a novel therapy for persistent pathologic pain.